LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desirable illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption. All factors considered, LED tube lamps are typically considered a cost-effective lighting option.
Typical LED tube lamps have a variety of LED lamp components and driving circuits. The LED lamp components include LED chip-packaging elements, light diffusion elements, high-efficiency heat dissipating elements, light reflective boards and light diffusing boards. LED lamps generate considerable amount of heat, which, if not properly dissipated, would shorten the life of the lamps or even destroy them. Problems including power loss, rapid light decay, and short lifetime due to poor heat dissipation are key considerations when improving the performance of the LED illuminating system. Heat dissipation is, therefore, an important issue when designing LED products.
Nowadays, most LED tube lamps use plastic tubes and metallic elements to dissipate heat from the LEDs. The metallic elements are usually exposed and are accessible by users from the outside of the plastic tubes. This design improves heat dissipation but heightens the risk of electric shocks. If we dispose metallic elements inside the plastic tubes, heat would be trapped inside the plastic tubes, which may be deformed through heat. Deformation of the plastic tubes also occurs even when the elements to dissipate heat from the LEDs are not metallic.
Metallic elements for dissipating heat from the LEDs may be made of aluminum. However, aluminum is too soft to sufficiently support the plastic tubes when deformation of plastic tubes occurs due to the heat as far as the metallic elements disposed inside the plastic tubes are concerned.
Present ways of using LED lamps such as LED tube lamps to replace traditional lighting devices (referring mainly to fluorescent lamps) include using a ballast-compatible LED tube lamp. Typically, there is no need to change the electrical or conductive wirings in traditional lamps, an LED tube lamp can be used to directly replace e.g. a fluorescent lamp. Common types of electronic ballast include instant-start ballast and program-start ballast. Electronic ballast typically includes an LC circuit and is designed to match the loading characteristics of a fluorescent lamp in driving the fluorescent lamp. For example, to properly start a fluorescent lamp, the electronic ballast provides driving methods respectively corresponding to the fluorescent lamp working as a capacitive device before emitting light, and working as a resistive device upon emitting light. LED is a nonlinear component with significantly different characteristics from a fluorescent lamp. Therefore, using an LED tube lamp with an electronic ballast impacts the design of the LC circuit of the electronic ballast, causing a compatibility problem.
Further, most of the circuit designs for LED tube lamps fail to provide suitable solutions to comply with relevant certification standards and for better compatibility with the driving structure using an electronic ballast originally for a fluorescent lamp. For example, since there are usually no electronic components in a fluorescent lamp, it is easy for a fluorescent lamp to be certified under EMI (electromagnetic interference) standards and safety standards for lighting equipment as provided by Underwriters Laboratories (UL). However, there are a considerable number of electronic components in an LED tube lamp. Therefore, consideration of the impacts caused by the layout (structure) of the electronic components is important, resulting in difficulties in complying with such standards.
Further, the driving of an LED uses a DC driving signal, but the driving signal for a fluorescent lamp is a low-frequency, low-voltage AC signal as provided by an AC powerline, a high-frequency, high-voltage AC signal provided by a ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp does not an LED tube lamp compatible with traditional driving systems of a fluorescent lamp.
In addition, for some LED tube lamps, rigid circuit board is typically electrically connected to the end caps by way of wire bonding, in which the wires may be easily damaged and even broken due to any move during manufacturing, transportation, and usage of the LED tube lamps and therefore may disable the LED tube lamps. Or, bendable circuit sheet may be used to electrically connect the LED assembly in the lamp tube and the power supply assembly in the end cap(s). The length of the lamp tube during manufacturing also needs to match for the bendable circuit sheet, and thus the variable factor increases in the manufacture of the lamp tube.
The heat generated by the LED tube lamp can be reduced by controlling the LED illumination and lighting period by an LED driving circuit. However, it is not easy to meet the expected LED illumination requirement based on some analog driving manners for two reasons. The relationship between the LED illumination and the LED current is non-linear. Moreover, color temperature of some LEDs changes in response to LED current. Furthermore, heat convection in the lamp tube is hindered, e.g., in some cases, the lamp tube is a closed space, and once the LED illumination increases, the lifespan of the LED tube lamp shortens because the lifespan of LEDs is sensitive to temperature. Also, some LED driving circuits result in the circuit bandwidth getting smaller since the driving voltage/current repeatedly returns between the maximum and minimum. This may limit the minimum conducting period and affects the driving frequency.
In addition, the LED tube lamp may be provided with power via two ends of the lamp and a user may be easily electric shocked when one end of the lamp is already inserted into a terminal of a power supply while the other end is held by the user to reach the other terminal of the power supply.
Currently applied techniques often fall short when attempting to address the abovementioned worse heat conduction, poor heat dissipation, heat deformation, electric shock, weak electrical connection, smaller driving bandwidth, and variable factor in manufacture defects.